Method of forming copper copper-oxide rectifier plates



- Io Drawing.

was May 16, 1930 .TYUNITEAD sT Tas PATENT OFFICE THEODORE ANDERSON, 33., AND LESTER rmcnm 313D, OI NEWARK, NEW 31538, ABSIGNOBS TO HANOVIA CHEMICAL AND IAHUTAGFUBING OI NEWARK, NEW JERSEY, A CORPORATION 01! NEW JERSEY METHOD OI'IOBHIN'G COPPER COPPER-OXIDE W PLATES Copper-copper oxide rectifier plates have been prepared in various ways; Ordinarily the method followed consisted in heating a prepared copper plate to a high temperature 5 m an oxidizing atmosphere, and producing a'la er of red oxide on the whole surface,

cooling the late somewhat in an oxidizing.

atmosphere uring which the surface of the red oxide is further oxidized causing the :0 formation of black oxide and then reducing in a reducing solution or liquid.

The action of the reducing agent was two fold. The black oxide formed by the oxidation of the red oxide during the cooling 15. process was reduced to copper and more or es of the surface of the red oxide was also reduced to copper. The copper formed was pecuharm that its molecular structure varied with the conditions under which it was pro;

:0 duced. As the structure could not be seen its exact character was not visually ascertainable but as soon as the rectifier plate was in-.

' serted in' an electric circuit the structure of the formed copper became apparent because of the resistance ofthe contact between it" and the oxide. I

Copper-copper oxide junctions exhibit very pecuhar properties that are not understood because'the molecular structure of the contact determines its electrical characteroccur and the contact'will behare like any The determinof the copper oxide. It seems that junctions formed'in the Y resenpe of concentrated reducing agents,yli e pure va ors, are rectifier-s, and junctions-formed in p ficiently dil to agents are non-rectifiers.

.Since the object, of the reducin to produceicopper on the outside 0 which does not for-ma rectiizi'ng contact with f in Y j the copper oxide, it must i conditlons that are capable of control as to v the copper so formed was an the wrong molece presence of suformed under concentration of the active material and without coming'in contact w th any pure acagent is the oxide Application fled August 80, 1988. Serlal Io. 808,188.

tive vapors. It will be immediately recognized that this condition is diflicult to secure. The copper oxide must be reduced at a fairly high temperature in order for the process to be successful. However, ifan active gas is formed by the reducing process and is present when the black oxide 1s reduced, the concentration of reducing agent iii the vapor is too high and .the formed copper will not be arranged in the proper molecular structure so that the efiiciency of the plate will be serious,- ly reduced. I p

The problem simplified comgonent parts involves the used an active re ucing agent that is non-volatile at a temperature approaching 500 C. B ber of organic acids, al which any skilled chemist recognizes as refar the larger numduci'n agents for hot copper oxide are very volati e at 500 C. and obtgously any solution of these in water will v latilize a few degrees above 100 C. 1

Aqueous s lutions of many ofthem will work with varying degrees of success especially a solution of wood alcohol in 7 water but this solution was found to be critical to the temperature of the plate when reduced and also criticalto the strength of the solution of alcohol. Moreover, it was found that the oxide on the copper plates was strained severely b the sudden cooling from 500 C. or therea uts to the temperature of the water and alcohol at about 20 C. In many cases the oxide was cracked and broken free from the copper. The rectifying contact is only secured by having the oxide adhere rigidly to the copper and any broken or loose crystals of the oxide that-might be present against. the copper at the junction produce serious leakage of the plates for current in {the reverse direction and'materially reduce the efiectiveness of the rectification.

Parafline oil was found to be fairly nonvolatile at about 500 C. but was so inactive hat it would not reduce-the copper oxide at this temperature. Successiul reductlon occurred at a somewhat higher temperature but notbelow the volatilization point and ular arrangement.

ehydes, alcohols etc.-

The answer apparently depended upon an activating agent that could be placed in the parafline so that the parafiine would be saturated with the vapor of the active material and the necessary reduction takes place below the temperature at which the parafline would react but still without any active vapor being formed. Several substances were found that would work in such a combination. Amongthese was hydrochinon. The solution of hydrochinon and parafline could be heated so that the vapor pressure of the hydrochinon in the parafline was appreciable and the activity of the solution was controlled by the temperature. The vapor pressure of-the hydrochinon was of course equal to atmospheric pressure'at 169 C... so that this was the limiting temperatures of the solution. The parafline becomes a liquid at about 70 C. so that. the rain e of possible operation lay between 70 and 169 C. z

It is well known that when. two liquids that are normally immiscible are in contact each difiuses somewhat into the other so that a vapor pressure of each is present inthe other. For this reason oil and water in conta'ct mix to a certain extent, air and water mix so that the water is saturated with air and the air with water vapor. Very few substances are soluble in parafline and at ordinary temperatures it is very inert chemically. owever, when arafline is melted and in contact with many hquid substances, with which no chemical reaction occurs, the vapor of the foreign substance penetrates the paraffine and exists in concentrations in it depending upon the temperature and pressure of the mixture. When an excess of the forei liquid is m contact with it the parafline .1s in a state of saturated 'e uilibrium with the foreign hguid vapor. his characteristic of vapor diffusion provides an almost ideal condition for a suitable reducing agent, in the treatment of the rectifier plates, because an active agent can be added to the parafline and only v the vapor of this ,agent exists in a very low concentration in the p e, moreover this concentration is controllable by variation of the operating tem rature. Certain of the alcohols, a dehy es, ketones, organic acids, and hydrocarbons the necessary characteristics forsatis actory operation as an. activating agent for a parafline reduc' solution. These characteristiw may be list ed as followsz- 1. The specific gravity at. 150 to 200 C. v

' must be above that of melted parafline at these temperatures sothe activegnaterial remains at the bottom of .the containing vessel. Otherwise the prepared copper plates would have to pm thru the active material to enter the parafline and so would be destroyed.

- 2. The substance mustbe'an active reduce ingagentsothatcopper 'cular structure of the 0 stance inactive with copper oxide to serve as 3. The boiling point of the substance should be about 150 C. or higher depending upon its activity as a reducing a nt. 1

4. The unwanted products of t e reaction between the active substance and the oxide should be gaseous at thetemperature of the solution and so boil ofi. When possible the reaction products should not be poisonous.

The use of the reducing methods described offers several distinct advantages as evidenced by the following summary.

FirstiThe nature of the contact between the reduced copper and the oxide is very vital and must be controlled so that the most eflicient bilateral contact is secured. The reducing materials and the methods described make such control ssible and exact.

Second: The activity of the reducing material is ordinarily dependent upon the temperature at which the oxidized rectifier plates are immersed. It has been shown that this may not be a satisfactory method since the temperature required for proper activity may be above that allowable to szpure proper moler ed copper. The reducing materials described present special advantages for this purpose since the activity of the reducing agent can be varied within itself and is not dependent upon a high temperature of the oxidized plate when immersed. v

Third: This reducing medium permits theuse of 'an active volatile material for the reducing agent without having the active gas of this material operating as an uncontrollable reducing agent. Only a. limited concentration of the active vapor can be active on any plate at any instant. Fourth: The reducin offers another distinct plates come out against moisture wit a complete .parafine coating. Suflicient parafline normally adheres to the plate so that it is sealed. This feature contributes somewhat toward ease of handling of the plates.

h i ii? a 1. at or re 11 co per oxide, comprising parafiine and li ydroc hinon, the erae serving as an inert vehicle to hol and distribute the hydrochinon.

2. A bath for reducing copper oxide, comrising parafiine-and a vapor of a hydrocarn reducing substance, the parafline serving as an inert .vehicle to hold anddistribute the reducing substance. T

In the manufacture of copper-copper oxide rectifier plates, a bath for reducing copper oxide to provide a film of metallic copper, said bath comprising hydrochinon and a submedium described vantage in that the sealed automatically a yehicle .to hold and distribute the hydrochmon.

4. In the manufacture of copper-copper oxide rectifier plates, the method of reducing copper oxide consisting of quenching in a bath of paraffine and hydrochinon.

5. A bath for reducing copper oxide, comprising paraffin, and a vapor ofa hydrocarbon derivative reducing substance, the paraflin serving as an inert vehicle to hold and dis tribute the reducing substance.

This specification signed this 17th day of August, 1928.

WILLIAM THEODORE ANDERSON, Jr. LESTER FLETCHER BIRD. 

